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Thursday, December 11, 2008

Unheralded Changes in ERSST.v3 Data

I’ve moved to WordPress.  This post can now be found at Unheralded Changes in ERSST.v3 Data
This’ll be a quick post with only two illustrations.

Back in an August 8 post, My Curse on Data Set Updates, I noted the lack of updates to the ERSST.v3 data. At that time, the data ended in April 2008. The updates resumed last month, but I didn’t think much about it, other than I was pleased that the newer data set had been made current. (I’ll remove that August 8 post in a few days, since both data sets resumed their updates.) Then, in a comment here, Bill Illis noted that he’d read a recent remark at another website about a change in SST data. Yesterday, I noticed a very minor change in the webpage address for the monthly global SST data. There was a “v3b” after the data set name, as in ersstv3b.
The old address for the same data excluded the “v3b”. (The following link no longer functions.)

Did version “B” include the “bucket correction” corrections? Refer to “A large discontinuity in the mid-twentieth century in observed global-mean surface temperature”, by Thompson et al (2008):http://www.nature.com/nature/journal/v453/n7195/abs/nature06982.html

NOPE! It doesn’t include them.

Figure 1 is a comparative graph of the ERSST.v3 (old) and ERSST.v3b (new) versions of the Global SST anomaly data. The data has been smoothed with a 37-month filter. There are very minor changes when viewing the global data set.
Figure 1

Subtracting the ERSST.v3 (old) from the ERSST.v3b (new) data presents a better view of the differences. Globally, the update appears to have created a very minor increase in trend, ~0.022 deg C per Century.
Figure 2

Are the corrections small changes in all oceans or are they major changes in small data sets such as the Arctic and Southern Oceans? The updates aren’t mentioned in the main page of the data set.

We’ll find out in a future post. (I haven’t a clue, but my guess is that the changes are in the high-latitudes of the Southern Hemisphere.)

Thanks to Bill Illis for calling my attention to the update.


…are included in text of post.


frank mosher said...

Bob, I check your blog daily and value your opinion. NINO 4 seems to have entered a persistent cool phase, on the weekly charts. Have you observed that? What do you think? Also, very warm temps off Labrador. Could they be caused by undersea geothermal activity? Frank Mosher

Bob Tisdale said...

Frank: The following is a link to the cross-sectional animation of the subsurface temperatures for the Equatorial Pacific. (You’ll have to cut and paste it to your browser. Links don’t post well in comments here.) They haven’t marked off the NINO longitudes in the graphic, but it doesn’t take much to figure out where they are. Unfortunately, there's the loss of data for the last period of the animation. (I assume that’s the reason for the “ENTIRE GRID UNDEFINED” at Dec 9.) If that large subsurface pool of cool water works its way to the surface, NINO temps will drop considerably.

I’ve read paper(s) about the hypothesis that undersea geothermal activity (and was it earth’s rotational eccentricities?) may have an impact on ENSO activity, but I haven’t spent any time trying to verify them. Can’t help you on that one.

Bob Tisdale said...

Let's try that website address again. Sorry. I had to break it twice to make it all come through.



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